This invention relates to gas treatment devices, such as filters or heat and moisture exchange devices (HMEs).
Medical filters and HMEs have a housing with couplings at opposite ends and a filter or HME element located in the housing, between its ends, so that gas flowing through the housing, between the couplings, passes through the element. These devices should have a maximum efficiency, with a minimum resistance to flow, a minimum dead space and low overall bulk. The dead space can be reduced by reducing the volume in the housing on either side of the element but this has the effect of hindering gas flow over the surface of the element, so that the gas flows mainly through the center of the element. In order to spread the gas flow more evenly over the element, devices often include a deflector located just above the element, in-line with the coupling on the inlet side, or, where the device is bidirectional, on both sides. The deflector has a conical or trumpet shape, as described in GB2231509, and is symmetrical about the axis of the device between the couplings. Such deflectors can improve the performance of those devices having a circular shape but, where the device is of a non-circular shape, such as rectangular or elliptical, the deflector may fail to distribute gas evenly to the outer parts of the element.